Snapshots

Open picture
Click on Background in Layers panel on the right and make a duplicate.
Select only the background copy.
Selest a portion of your picture by using the crop tool from the tool bar
Add a new layer by clicking the icon below the panels 3rd from the left,
Add some circles by clicling on the tool under the arrow tool on the left. Click down the left mouse button then click the elipse tool.
Click and drag to make the circles.
Add some rectangles from the same tool.
Add a new layer
To change the colour of new shapes, click on the coloured square in the options bar.
Open history panel
Window - History
Chose a part you want to look at and take a snapshot by clicking on the camera icon at the bottom of the history panel.
The picture appears at the top of the history panel.